The present invention relates to an ink jet print head of a thermal type that air bubbles are produced in ink due to the heat that is generated by a heating element and the ink is jetted out due to the pressure of the thus produced air bubbles, thereby carrying out recording.
Conventionally, as an ink jet print head of a thermal type, there have been developed a side shooter type and a roof shooter type. The ink jet print head of a side shootor type is a head of a type that a heating element is disposed in the intermediate portion of an ink flow passage and ink is jetted out in a direction parallel to the surface of the heating element. With use of the print head of a side shooter type, for example, as shown in the Unexamined Japanese Patent Application Publication No. Sho 61-230954, the Examined Japanese Patent Application Publication No. Hei 6-98758, the Examined Japanese Patent Application Publication No. Hei 6-98763, and the like, an anisotropic etching is enforced in a Si substrate to thereby be able to form an injection port for ink. That is, a side shooter type is suitable for a high-density print head.
On the other hand, the print head of a roof shooter type is structured such that ink is jetted out. from an injection port, which is formed in a surface opposed to the surface of a heating element, in a direction at right angles to the surface of the heating element. The print head having this structure is disclosed in the Examined Japanese Patent Application Publication No. Hei 6-4320, the Examined Japanese Patent Application Publication No. Hei 7-29437, the Unexamined Japanese Patent Application Publication No. Hei 6-79874, and the like. According to this type of print head, a high injection efficiency can be obtained, the print head can he driven at high frequencies, and a strong injection force can be provided. On the other hand, however, the print head of a roof shooter type is disadvantageous in that it is unable to provide a highly dense arrangement of the injection ports per line. For this reason, the injection ports are arranged in a plurality of lines in order to be able to enhance the recording density thereof.
Further, as disclosed in the Examined Japanese Patent Application Publication No. Sho 63-6356, the Unexamined Japanese Patent Application Publication No. Sho 55-59975, and the like, there is also known another structure in which a heating element is disposed in the intermediate portion of an ink slow passage as in the print head of a side shooter type and the surface of the heating element is directed toward ink injection ports as in the print head of a roof shooter type.
As an example of the ink jet print head of a roof shooter type, for instance, in the Unexamined Japanese Patent Application Publication No. Hei 6-79874, there is disclosed a structure in which a tape member includes a member having an orifice and an ink flow passage. Also, in the Unexamined Japanese Patent Application Publication No. Hei 6-8434, there is disclosed a print head of a roof shooter type which is the same in structure as in the above publication and also which further includes a fluid channel structure for jetting out ink from an ink tank through the back, side and upper surfaces of a substrate carrying a heating element thereon. Further, in the Unexamined Japanese Patent Application Publication No. Hei 6-8472, there is disclosed a seal structure for a flow passage disclosed in the Unexamined Japanese Patent Application Publication No. Hei 6-8434 and, in an embodiment thereof, there is illustrated a flow passage structure in which tape having injection ports formed therein is connected to a barrier layer. Still further, in the specification of U.S. Pat. No. 4,794,411, there is disclosed a heating element which is formed square. Moreover, in the Unexamined Japanese Patent Application Publication No. Hei 7-1739, there is disclosed a method for manufacturing such ink jet print head.
However, in the above-mentioned conventional ink jet print heads, for example, when trying to realize a higher density such as 600 dpi or more, or when trying to enhance the drive frequencies of the individual channels and, at the same time, to increase the number of drive bits to thereby realize a higher speed, there arise the following problems. At first, the dimensions of the injection ports in the arrangement direction thereof are reduced so that the freedom of design of the injection ports is lowered, and it is difficult to secure the strength of the part in which the injection ports are formed. For example, in the structures as set forth in the above-mentioned publications, a photosensitive resin layer is used as an ink flow passage, while the ink flow passage, in particular, the ink flow side of the ink flow passage onto the heating element is reduced in size in the direction of arrangement of the injection ports in order to prevent the ink from flowing backward. Provision of such size reduction structure not only makes it difficult to secure a sufficient resolution for etching of the photosensitive resin, but also reduces the cross section of the flow-in side of the ink flow passage to thereby increase the resistance of the ink flow passage. Also, in the structure in which the ink supply passage is so formed as to extend around the back portion, end portion and upper portion of the substrate with the heating element carried thereon, If the injection ports are increased in number and the substrate is thereby extended in length, then the support of the back surface of the substrate is short, with the result that the substrate itself becomes weak in strength and thus it can be broken easily. Further, a distance from the heating element to the injection port is preferably about 100 .mu.m or less from the viewpoint of a jetting performance and, in the above-mentioned publications as well, the distance is controlled down to about 75 .mu.m because the injection ports are formed in the tape member. However, the tape member is short of strength as a component of the print head.
In order to enhance the strength of a component in which the injection ports are to be formed, for example, in the Examined Japanese Patent Application Publication No. Hei 6-4320 and FIGS. 10A and 11 of the specification of U.S. Pat. No. 4,490,728, there is disclosed a structure in which a rather thick plate is used and there are formed recessed portions in the ink injection port surfaces of the plate. However, in such structure in which the ink injection port surfaces are simply recessed suddenly, there arises a problem that, when the ink injection ports are wiped in maintenance, they cannot be cleaned up.
By the way, as a method for reducing the size of the ink flow passage on the ink flow-in side thereof onto the heating element, not in the print head of a roof shooter type but in the print head of a side shooter type, for example, as disclosed in the Unexamined Japanese Patent Application Publication No. Sho 55-100169 and the Unexamined Japanese Patent Application Publication No. Sho 60-204352, there is known a method in which a barrier layer is provided on the ink flow-in side of the ink flow passage so as to enhance the jetting performance of ink, or, as disclosed in the Unexamined Japanese Patent Application Publication No. Hei 7-232433, the Japanese Patent Application No. Hei 7-112097, and the like, there is known a method in which the cross section of an ink flow passage formed in a synthetic resin layer is reduced not only in the arrangement direction of injection ports but also in directions respectively at right angles to the arrangement direction of the injection ports and to the direction of flow of ink. On the other hand, in the print head of a roof shooter type, as disclosed in the specification of U.S. Pat. No. 4,558,333, there is known a structure in which heating elements are respectively separated by partition walls to thereby prevent the pressure from being propagated in other directions than the direction of the injection ports.
Further, as a structure of a roof shooter type, for example, there is known a structure in which the size of the ink flow passage is reduced in the arrangement direction of injection ports but, as disclosed in the specification of U.S. Pat. No. 5,455,613, a pressure chamber in which a heating element is formed is formed in a circular or elliptical shape. In this case as well, the resolution for etching the photosensitive resin cannot be enhanced. Still further, as disclosed in the Unexamined Japanese Patent Application Publication No. Hei 5-31898, there is known a structure in which no such size reduced portion is provided in an ink flow passage but a rectangular pressure chamber is, as it is, connected to a common ink flow passage. In this case, however, the pressure propagation to other directions than that of the injection ports cannot be avoided.
Now, referring to the structure of a nozzle, for example, as disclosed in the Unexamined Japanese Patent Application Publication No. Hei 6-328699 as well as in the before-mentioned Unexamined Japanese Patent Application Publication No. Hei 5-31898, there is known a structure in which the nozzle is tapered. However, in an ink jet print head disclosed in the Unexamined Japanese Patent Application Publication No. Hei 6-328699, similarly to the above-mentioned roof shooter type, some of nozzles are formed in tape member or the like so that such nozzles are lacking in strength from the viewpoint of the parts of an ink print head. Also, more preferably, the whole of the upper portion of the heating element may be tapered but it is impossible to provide such taper in the barrier layer.
Referring to the structure of an ink flow passage, there are known several structures for example, a structure in which an ink flow passage starts from the back side of a substrate with a heating element placed thereon, passes through the side portion thereof, and then arrives at the top surface thereof, as disclosed in the above-mentioned Unexamined Japanese Patent Application Publication No. Hei 6-8434; a structure in which there are opened up holes in a substrate and ink is supplied through the holes, that is, from both sides of a heating element onto the top surface of the heating element, as disclosed in the Unexamined Japanese Patent Application Publication No. Sho 60-206653; and, a structure in which there is opened up a hole between two heating elements, and ink is supplied from the hole and is diverged to two sides so that the ink can be supplied onto the respective top surfaces of the two heating elements. However, because the substrate on which the heating element is carried is hard, in the method to open up a hole in the substrate, it is not easy to machine the substrate to open up the hole in the substrate and also such machining operation inevitably has an ill effect on the substrate.
In a structure disclosed in the Unexaminied Japanese Patent Application Publication No. Sho 63-183855, a substrate on which two heating elements are placed is disposed on the two sides of an elliptic hole formed in a base member, that is, without opening up a hole in the substrate, there can be obtained a similar structure to the above-mentioned Unexamined Japanese Patent Application Publication No. Hei 7-144418. However, in such structure, similarly to the above-mentioned structure using the tape member, a sufficient strength cannot be secured for a member in which injection ports are formed. Also, when a metal plate formed of metal such as Al or the like is used as the base member, it gives an advantage to radiation of heat but, since the metal plate provides a flow passage for ink, it is exposed to the ink and is thereby easy to corrode.
Further, as illustrated in the above-mentioned Unexamined Japanese Patent Application Publication No. Hei 5-31898, there is proposed a structure in which an opening is formed in an ink tank cover, a head chip is fixed in such a manner that the head chip covers the opening, and a top plate is placed on the head chip. However, in this structure, because the head chip is not in contact with the metal plate formed of metal such as Al or the like, radiation of heat is poor, so that the performance and durability of the structure are poor. If the ink tank cover is formed of metal such as Al or the like, then good heat radiation can be provided but, because the ink tank cover is part of the ink tank, the ink tank cover is always in contact with ink, so that the ink tank cover can be corroded as described above.
Referring now to a method for manufacturing an ink jet print head using a similar technique to the prosent invention, for example, in the Unexamined Japanese Patent Publication No. Hei 7-223316, a nozzle plate blank material is injection molded and a nozzle is machined by us of laser. Also, in the Unexamined Japanese Patent Application Publication No. Hei 2-121843 and U.S. Pat. No. 5,208,604, after the outer shape of a top plate, individual flow passages and the like are formed by use of a resin mold, a nozzle is formed by use of laser. However, these techniques are used to manufacture an ink jet print head of a side shooter type, but not to manufacture an ink jet print head of a roof shooter type.
Now, according to the specification of U.S. Pat. No. 4,528,577, in an ink jet print head of a roof shooter type, an ink flow passage and a nozzle are formed in an orifice plate using an electro-forming method which is different from the method of the present invention. Also, according to the specification of U.S. Pat. No. 5,291,226, an ink flow passage and a nozzle are formed in a tape member by use of laser. The laser machining operation is truly able to machine such flow passage and nozzle with high precision but, disadvantageously, it takes much time to machine the whole shape of the flow passage and nozzle by laser. Further, in the above-mentioned Unexamined Japanese Patent Application Publication No. Hei 7-144418, the nozzle, flow passage and the like are formed in an integral manner. The integral formation does not require additional machining, whereas the integral formation has a limit to fine or minute machining.